How can I make the default size of new objects 1 x 1?
You can achieve stuff like this by setting a custom scale value to the grid itself. I'm working in metric system on my machine and have my scale value set to 0.1, which results in the cube being added having a length of 20 centimeters instead of 2 meters. For imperial, you can set it up like this:


set your units to Imperial in the Scene tab. This sets your main units to feet.





Calculate a working scale factor for converting feet to inches, and enter it in the N Panel in the 3D Viewport




If I am not mistaken, feet and inches have a relation of 1:12. So the multiplier will be 0.08333333


Save your Startup File using Ctrl + U
Restart Blender, as this only takes effect after doing so


Test it by adding a new cube. It should be exactly 2 inches wide. Note that the grid lines now are also 1 inch apart each.